Chapter 5.5, Problem 29PPS

To determine

To find: the value of c that makes perfect square and write the trinomial as a perfect square.

Answer to Problem 29PPS

The value of $\text{c=}\frac{81}{4}$ and perfect square is ${\left(\text{x+}\frac{9}{2}\right)}^2$ .

Explanation of Solution

Given:

  ${\text{x}}^{\text{2}}\text{+9x+c}$ .

Concept used:

An expression obtained from the square of binomial equation is a perfect square trinomial is in the form of ${\text{ax}}^{\text{2}}\text{+bx+c}$ is said to be a perfect square, if only if it satisfies the condition ${\text{b}}^{\text{2}}\text{=4ac}$ .

The perfect squares trinomial formula is given as:

  ${\left(\text{ax}\right)}^{\text{2}}{\text{+2abx+b}}^{\text{2}}\text{=}{\left(\text{ax+b}\right)}^{\text{2}}$ .

  ${\left(\text{ax}\right)}^{\text{2}}{\text{-2abx+b}}^{\text{2}}\text{=}{\left(\text{ax-b}\right)}^{\text{2}}$

Calculation:

  ${\text{x}}^{\text{2}}\text{+9x+c}$ .

To make the trinomial a perfect square, find the value of $\text{c}$ .

First Find the half of the coefficient of second term:

. $\frac{9}{2}$

Square the result of the half of the coefficient of the second term will be the $\text{c}$ :

  $\text{c=}\frac{81}{4}$ .

The trinomial ${\text{x}}^{\text{2}}\text{+9x+}\frac{81}{4}$

can be written as:

  $\Rightarrow {\text{x}}^{\text{2}}\text{+2}\left(\text{x}\right)\left(\frac{1}{2}.9\right)\text{+}{\left(\frac{9}{2}\right)}^2\text{-}{\left(\frac{9}{2}\right)}^2+\frac{81}{4}$ .

  $\Rightarrow {\left(\text{x+}\frac{9}{2}\right)}^2$ .

Hence the value of $\text{c=}\frac{81}{4}$ and perfect square is ${\left(\text{x+}\frac{9}{2}\right)}^2$ .